The present invention relates to a solid relay and a method of producing the same and, more particularly, to a solid relay having a light emitter and a photodetector in an unitary configuration and easy to produce, and a method of producing the same.
Japanese Patent Laid-Open Publication No. 58-213481 teaches a photocoupler whose structure is closest to the above light emitter and photodetector constructed integrally with each other. To produce the photocoupler, ternary AlGaAs mixed crystal semiconductor layers each having a thickness of less than several ten microns inclusive are formed on a GaAs crystal substrate by liquid-phase epitaxial growth. Specifically, an N type AlGaAs layer is formed on the major surface of the GaAs crystal substrate. Then, P type AlGaAs layers and N type AlGaAs layers are formed on the above N type AlGaAs layer alternately with each other. The resulting four- or five-layer block constitute a light emitter and a photodetector.
However, the photocoupler having the above configuration has some problems left unsolved although its light emitter and photodetector are formed integrally with each other. First, the light emitter and photodetector are not separate from each other as to insulation. Second, use cannot be made of an Si device predominant over compound semiconductor devices in characteristic, stability and cost and extensively used. Third, considering semiconductor devices in general, the photocoupler needs a special crystal material and a special production process, i.e., exclusive facilities and production line.
In the art of solid relays to which the present invention pertains, it is a common practice to separate a GaAs light emitter (light emitting diode or LED) and an Si photodetector (photodiode or phototransistor) and optically couple them during assembly or packaging.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 61-225879 and 63-208322.